This disclosure relates to an orifice for venting a reservoir and promoting thermal stabilization of a pumping system.
Reservoirs are commonly used in various fluid systems for accommodating thermal expansion of the fluid and providing a reserve of fluid to make up for any leakage from the system. In pressurized reservoirs, the presence of an excessive amount of air can be problematic for maintaining pressure and obtaining accurate fluid level measurements. Therefore, it is necessary to periodically manually vent the reservoir to remove any accumulated air.
One type of pressurized reservoir is a bootstrap reservoir, which employs the discharge from a pump that circulates the fluid to increase fluid pressure at the pump inlet. In a bootstrap reservoir, a double ended piston is actuated by a pump discharge pressure and in turn pressurizes fluid at the pump inlet.
In many current bootstrap reservoir systems, the reservoir is not an active part of the flow circuit. That is, the fluid within the reservoir is typically in an essentially static state and the only fluid movement into or out of the reservoir is in response to thermal expansion of the fluid or, more rarely, in response to leakage occurring in the external circuit. Systems operating in extreme environmental conditions, for example, during high-altitude flight of an aircraft, can exhibit a large difference in the temperature of the fluid in an actively flowing circuit of the system and that of the fluid in the reservoir.
In a sudden event, such as a major leak or other system flow demand, cold fluid exiting the reservoir can impose a thermal shock on other parts of the system, which may have undesirable effects. Further, if the reservoir temperature is significantly lower than that of the main bulk fluid, increased viscosity of the colder reservoir fluid may reduce the dynamic response of the reservoir, causing insufficient and slow supply of fluid to the operating system. If the pressure in the system becomes too low or there is not enough fluid in the system, the pump(s) may operate inefficiently or be damaged by cavitation.
Additionally, air may become trapped in the bootstrap reservoir and can act as a compressible spring on the piston. Fluctuations in the reservoir environment, such as the ambient temperature, can change the properties of the air and cause the piston to move, which can in turn cause pressure fluctuations throughout the system. Current reservoir designs can be difficult to vent due to the lack of accessibility to the chambers once the system is installed in the aircraft or other machine.